Table
7-2:
Priority of Playfields Based on Values of Bits PF1P2-PF1PO
Value
Placement
(from
most
important
to
least
important)
000 PF1
SP01 SP23
SP45 SP67
001
SP01
PF1 SP23 SP45
SP67
010 SP01
SP23
PF1
SP45 SP67
011
SP01
SP23 SP45 PF1
SP67
100
SP01
SP23
SP45
SP67 PF1
In this table, PF1 stands for playfield
1,
and SP01
stands
for the group of sprites num-
bered 0 and
1. SP23 stands for sprites 2 and 3 as a group; SP45
stands
for sprites 4 and
5 as a group; and SP67 stands for sprites 6 and 7 as a group.
Bits PF2P2-PF2PO let you position play
field
2 among the sprite priorities in exactly the
same way. However, it is the PF2PRI bit
that
determines which of the two playfields
appears in front of the other on the screen. Here is a sample of possible BPLCON2
register contents
that
would create something a little unusual:
BITS 15-7
PF2PRI
PF2P2-0 PF1P2-0
VALUE
Os
1 010 000
This will result
in
a sprite/playfield priority placement
of:
PF1 SP01 SP23 PF2 SP45 SP67
In other words, where objects pass across each other, playfield 1
is
in
front of sprite 0
or
1;
and sprites 0 through 3 are
in
front of playfield
2.
However, playfield 2
is
in
front of
playfield 1 in any area where they overlap and where playfield 2 is
not
blocked by sprites
o through 3.
System Control Hardware
201
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